diff options
Diffstat (limited to 'plugins/Pcre16/docs/doc/html/pcrecallout.html')
| -rw-r--r-- | plugins/Pcre16/docs/doc/html/pcrecallout.html | 286 |
1 files changed, 0 insertions, 286 deletions
diff --git a/plugins/Pcre16/docs/doc/html/pcrecallout.html b/plugins/Pcre16/docs/doc/html/pcrecallout.html deleted file mode 100644 index 53a937f52d..0000000000 --- a/plugins/Pcre16/docs/doc/html/pcrecallout.html +++ /dev/null @@ -1,286 +0,0 @@ -<html> -<head> -<title>pcrecallout specification</title> -</head> -<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> -<h1>pcrecallout man page</h1> -<p> -Return to the <a href="index.html">PCRE index page</a>. -</p> -<p> -This page is part of the PCRE HTML documentation. It was generated automatically -from the original man page. If there is any nonsense in it, please consult the -man page, in case the conversion went wrong. -<br> -<ul> -<li><a name="TOC1" href="#SEC1">SYNOPSIS</a> -<li><a name="TOC2" href="#SEC2">DESCRIPTION</a> -<li><a name="TOC3" href="#SEC3">MISSING CALLOUTS</a> -<li><a name="TOC4" href="#SEC4">THE CALLOUT INTERFACE</a> -<li><a name="TOC5" href="#SEC5">RETURN VALUES</a> -<li><a name="TOC6" href="#SEC6">AUTHOR</a> -<li><a name="TOC7" href="#SEC7">REVISION</a> -</ul> -<br><a name="SEC1" href="#TOC1">SYNOPSIS</a><br> -<P> -<b>#include <pcre.h></b> -</P> -<P> -<b>int (*pcre_callout)(pcre_callout_block *);</b> -</P> -<P> -<b>int (*pcre16_callout)(pcre16_callout_block *);</b> -</P> -<P> -<b>int (*pcre32_callout)(pcre32_callout_block *);</b> -</P> -<br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br> -<P> -PCRE provides a feature called "callout", which is a means of temporarily -passing control to the caller of PCRE in the middle of pattern matching. The -caller of PCRE provides an external function by putting its entry point in the -global variable <i>pcre_callout</i> (<i>pcre16_callout</i> for the 16-bit -library, <i>pcre32_callout</i> for the 32-bit library). By default, this -variable contains NULL, which disables all calling out. -</P> -<P> -Within a regular expression, (?C) indicates the points at which the external -function is to be called. Different callout points can be identified by putting -a number less than 256 after the letter C. The default value is zero. -For example, this pattern has two callout points: -<pre> - (?C1)abc(?C2)def -</pre> -If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled, PCRE -automatically inserts callouts, all with number 255, before each item in the -pattern. For example, if PCRE_AUTO_CALLOUT is used with the pattern -<pre> - A(\d{2}|--) -</pre> -it is processed as if it were -<br> -<br> -(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) -<br> -<br> -Notice that there is a callout before and after each parenthesis and -alternation bar. If the pattern contains a conditional group whose condition is -an assertion, an automatic callout is inserted immediately before the -condition. Such a callout may also be inserted explicitly, for example: -<pre> - (?(?C9)(?=a)ab|de) -</pre> -This applies only to assertion conditions (because they are themselves -independent groups). -</P> -<P> -Automatic callouts can be used for tracking the progress of pattern matching. -The -<a href="pcretest.html"><b>pcretest</b></a> -program has a pattern qualifier (/C) that sets automatic callouts; when it is -used, the output indicates how the pattern is being matched. This is useful -information when you are trying to optimize the performance of a particular -pattern. -</P> -<br><a name="SEC3" href="#TOC1">MISSING CALLOUTS</a><br> -<P> -You should be aware that, because of optimizations in the way PCRE compiles and -matches patterns, callouts sometimes do not happen exactly as you might expect. -</P> -<P> -At compile time, PCRE "auto-possessifies" repeated items when it knows that -what follows cannot be part of the repeat. For example, a+[bc] is compiled as -if it were a++[bc]. The <b>pcretest</b> output when this pattern is anchored and -then applied with automatic callouts to the string "aaaa" is: -<pre> - --->aaaa - +0 ^ ^ - +1 ^ a+ - +3 ^ ^ [bc] - No match -</pre> -This indicates that when matching [bc] fails, there is no backtracking into a+ -and therefore the callouts that would be taken for the backtracks do not occur. -You can disable the auto-possessify feature by passing PCRE_NO_AUTO_POSSESS -to <b>pcre_compile()</b>, or starting the pattern with (*NO_AUTO_POSSESS). If -this is done in <b>pcretest</b> (using the /O qualifier), the output changes to -this: -<pre> - --->aaaa - +0 ^ ^ - +1 ^ a+ - +3 ^ ^ [bc] - +3 ^ ^ [bc] - +3 ^ ^ [bc] - +3 ^^ [bc] - No match -</pre> -This time, when matching [bc] fails, the matcher backtracks into a+ and tries -again, repeatedly, until a+ itself fails. -</P> -<P> -Other optimizations that provide fast "no match" results also affect callouts. -For example, if the pattern is -<pre> - ab(?C4)cd -</pre> -PCRE knows that any matching string must contain the letter "d". If the subject -string is "abyz", the lack of "d" means that matching doesn't ever start, and -the callout is never reached. However, with "abyd", though the result is still -no match, the callout is obeyed. -</P> -<P> -If the pattern is studied, PCRE knows the minimum length of a matching string, -and will immediately give a "no match" return without actually running a match -if the subject is not long enough, or, for unanchored patterns, if it has -been scanned far enough. -</P> -<P> -You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE -option to the matching function, or by starting the pattern with -(*NO_START_OPT). This slows down the matching process, but does ensure that -callouts such as the example above are obeyed. -</P> -<br><a name="SEC4" href="#TOC1">THE CALLOUT INTERFACE</a><br> -<P> -During matching, when PCRE reaches a callout point, the external function -defined by <i>pcre_callout</i> or <i>pcre[16|32]_callout</i> is called (if it is -set). This applies to both normal and DFA matching. The only argument to the -callout function is a pointer to a <b>pcre_callout</b> or -<b>pcre[16|32]_callout</b> block. These structures contains the following -fields: -<pre> - int <i>version</i>; - int <i>callout_number</i>; - int *<i>offset_vector</i>; - const char *<i>subject</i>; (8-bit version) - PCRE_SPTR16 <i>subject</i>; (16-bit version) - PCRE_SPTR32 <i>subject</i>; (32-bit version) - int <i>subject_length</i>; - int <i>start_match</i>; - int <i>current_position</i>; - int <i>capture_top</i>; - int <i>capture_last</i>; - void *<i>callout_data</i>; - int <i>pattern_position</i>; - int <i>next_item_length</i>; - const unsigned char *<i>mark</i>; (8-bit version) - const PCRE_UCHAR16 *<i>mark</i>; (16-bit version) - const PCRE_UCHAR32 *<i>mark</i>; (32-bit version) -</pre> -The <i>version</i> field is an integer containing the version number of the -block format. The initial version was 0; the current version is 2. The version -number will change again in future if additional fields are added, but the -intention is never to remove any of the existing fields. -</P> -<P> -The <i>callout_number</i> field contains the number of the callout, as compiled -into the pattern (that is, the number after ?C for manual callouts, and 255 for -automatically generated callouts). -</P> -<P> -The <i>offset_vector</i> field is a pointer to the vector of offsets that was -passed by the caller to the matching function. When <b>pcre_exec()</b> or -<b>pcre[16|32]_exec()</b> is used, the contents can be inspected, in order to -extract substrings that have been matched so far, in the same way as for -extracting substrings after a match has completed. For the DFA matching -functions, this field is not useful. -</P> -<P> -The <i>subject</i> and <i>subject_length</i> fields contain copies of the values -that were passed to the matching function. -</P> -<P> -The <i>start_match</i> field normally contains the offset within the subject at -which the current match attempt started. However, if the escape sequence \K -has been encountered, this value is changed to reflect the modified starting -point. If the pattern is not anchored, the callout function may be called -several times from the same point in the pattern for different starting points -in the subject. -</P> -<P> -The <i>current_position</i> field contains the offset within the subject of the -current match pointer. -</P> -<P> -When the <b>pcre_exec()</b> or <b>pcre[16|32]_exec()</b> is used, the -<i>capture_top</i> field contains one more than the number of the highest -numbered captured substring so far. If no substrings have been captured, the -value of <i>capture_top</i> is one. This is always the case when the DFA -functions are used, because they do not support captured substrings. -</P> -<P> -The <i>capture_last</i> field contains the number of the most recently captured -substring. However, when a recursion exits, the value reverts to what it was -outside the recursion, as do the values of all captured substrings. If no -substrings have been captured, the value of <i>capture_last</i> is -1. This is -always the case for the DFA matching functions. -</P> -<P> -The <i>callout_data</i> field contains a value that is passed to a matching -function specifically so that it can be passed back in callouts. It is passed -in the <i>callout_data</i> field of a <b>pcre_extra</b> or <b>pcre[16|32]_extra</b> -data structure. If no such data was passed, the value of <i>callout_data</i> in -a callout block is NULL. There is a description of the <b>pcre_extra</b> -structure in the -<a href="pcreapi.html"><b>pcreapi</b></a> -documentation. -</P> -<P> -The <i>pattern_position</i> field is present from version 1 of the callout -structure. It contains the offset to the next item to be matched in the pattern -string. -</P> -<P> -The <i>next_item_length</i> field is present from version 1 of the callout -structure. It contains the length of the next item to be matched in the pattern -string. When the callout immediately precedes an alternation bar, a closing -parenthesis, or the end of the pattern, the length is zero. When the callout -precedes an opening parenthesis, the length is that of the entire subpattern. -</P> -<P> -The <i>pattern_position</i> and <i>next_item_length</i> fields are intended to -help in distinguishing between different automatic callouts, which all have the -same callout number. However, they are set for all callouts. -</P> -<P> -The <i>mark</i> field is present from version 2 of the callout structure. In -callouts from <b>pcre_exec()</b> or <b>pcre[16|32]_exec()</b> it contains a -pointer to the zero-terminated name of the most recently passed (*MARK), -(*PRUNE), or (*THEN) item in the match, or NULL if no such items have been -passed. Instances of (*PRUNE) or (*THEN) without a name do not obliterate a -previous (*MARK). In callouts from the DFA matching functions this field always -contains NULL. -</P> -<br><a name="SEC5" href="#TOC1">RETURN VALUES</a><br> -<P> -The external callout function returns an integer to PCRE. If the value is zero, -matching proceeds as normal. If the value is greater than zero, matching fails -at the current point, but the testing of other matching possibilities goes -ahead, just as if a lookahead assertion had failed. If the value is less than -zero, the match is abandoned, the matching function returns the negative value. -</P> -<P> -Negative values should normally be chosen from the set of PCRE_ERROR_xxx -values. In particular, PCRE_ERROR_NOMATCH forces a standard "no match" failure. -The error number PCRE_ERROR_CALLOUT is reserved for use by callout functions; -it will never be used by PCRE itself. -</P> -<br><a name="SEC6" href="#TOC1">AUTHOR</a><br> -<P> -Philip Hazel -<br> -University Computing Service -<br> -Cambridge CB2 3QH, England. -<br> -</P> -<br><a name="SEC7" href="#TOC1">REVISION</a><br> -<P> -Last updated: 12 November 2013 -<br> -Copyright © 1997-2013 University of Cambridge. -<br> -<p> -Return to the <a href="index.html">PCRE index page</a>. -</p> |